main factors affecting the quality of PZT piezoelectric ceramics
PZT piezoelectric ceramics have high Curie temperature due to the piezoelectric strong, easy doping, good stability, since the 1960s, has been the focus of attention and research in the field of piezoelectric ceramics dominant.
The preparation of PZT piezoelectric ceramics, the PZT powder synthesis and sintering densification PZT greatest impact on product quality.
PZT powders with fine particle size, surface area, reactivity advantages, can reduce the sintering temperature, reducing lead volatilization, ensure accurate stoichiometric PZT improve product performance, thus preparing ultrafine PZT powders have become PZT piezoelectric ceramics focus of the study.
In recent years the study of ultrafine powder preparation of PZT developed many new methods. In addition to the traditional solid-phase method of solid-phase method, also includes microwave radiation, mechanical chemical reaction sintering method. With a low temperature liquid phase synthesis, simple equipment, easy operation, low cost, have been used to prepare PZT powders, such as sol-gel method, hydrothermal method, precipitation method.
But Preparation and Properties of PZT piezoelectric ceramics are still many deficiencies, including: Powder reunion, chemical products, performance measurement and easy to aging.
1 Powder reunion: generally include soft and hard reunion reunion. Soft agglomerates due to the particle size of the powder decreases, van der Waals forces between the particles, and capillary force of the electrostatic attraction, and enhance the interaction between the formation; hard agglomerates due to hydrogen bonding groups chemically bound between OH- [2OH H2O (g) + O2-] formation of a bridging oxygen bond, a bridge oxygen bond interaction between the particles is formed.
Reunion ultrafine PZT powders to be the most important factor reflects the excellent performance, but also greatly affect the quality of PZT products. This is due to the PZT material belonging to the functional material that the basic requirements for synthetic powders are: high purity, ultra-fine particle size distribution, dispersion, chemical doping of uniform and accurate measurement.
In addition, PZT powder synthesis reunion will result in uneven emergence decreased bulk density and morphology, and the introduction of a large number of pores and lead to uneven microstructure seriously affected products low PZT piezoelectric, thermoelectric performance. Therefore, to reduce or prevent the synthesis of ultrafine powders of PZT reunion is to prepare high performance PZT piezoelectric ceramic premise.
Preparation of PZT powders reunion including soft and hard reunite two kinds of forms. Powders for different preparation methods, reunion mechanism is different. Traditional solid-phase synthesis of PZT powder, the process is characterized by the need to repeatedly milling and calcination temperature is high, repeated milling not only easy to introduce impurities, and too easily lead to the formation of grinding reunion, especially in recent years the development of mechano-chemical method is the use of mechanical energy to complete; calcination temperature is too high may cause the powder reunion.
Using liquid phase into the whole PZT powder, liquid generated due to the solid phase particles generally after nucleation, growth, coalescence, agglomeration process. Thus the structure can be formed by polymerization to: when one liquid phase to form a solid phase particles, since the movement under the action of Brown, particles approach each other, when the kinetic energy of the particles is greater than the potential barrier is formed between the aggregates, between the particles Brown in the role of sport and mutual reunion; Second, in the solid-liquid separation process, with the exclusion of the last part of the liquid phase, due to the surface tension of the solid-phase particles are close to each other and come together.
In particular, the synthesis of PZT powders using water as solvent, the final residue in a minimum amount of water between the particles and the particles through the hydrogen bonding of the particles to stick together tightly. In addition, PZT precursor powder prepared generally in the 500 ~ 700 ℃ calcined powders may also lead to reunite, but also enables the formation of aggregates has been aggravated due to partial sintering to form aggregates structure.
Visible to coprecipitation PZT powders, co-precipitation, grain growth to precipitate rinsing, drying, calcination of each section may result in the formation of particles and aggregates grow.
According to the causes reunion, reduce or avoid the preparation of ultrafine particles PZT powders can grow up and reunite from the following considerations:
First, the nucleation and growth process of separation and promote nucleation and controlled growth; ensure nucleation rate greater than the growth rate, which is generated to ensure the PZT precursor powder in the larger degree of supercooling or high supersaturation.
